The present invention relates to a polymer which comprises at least one structural unit which contains at least one aldehyde group, and to a process for the preparation of a crosslinkable and/or crosslinked polymer including a polymer which contains aldehyde groups. The process according to the invention for the preparation of a crosslinked polymer including a polymer containing aldehyde groups results in polymers having an excellent degree of crosslinking. The present invention thus also relates to a crosslinked polymer which is prepared by the process according to the invention, to the use of this crosslinked polymer in electronic devices, in particular in organic electroluminescent devices, so-called OLEDs (OLED=organic light emitting diode), and to organic electroluminescent devices comprising this crosslinked polymer. The present invention also relates to the use of the polymer containing aldehyde groups according to the invention for the preparation of a polymer containing vinyl or alkenyl groups or of a crosslinked polymer.
In opto-electronic devices, such as OLEDs, in particular PLEDs (polymeric light emitting diodes), components having different functionalities are required. In PLEDs, the different functionalities are normally present in different polymer layers. In this case, the term multilayered OLED systems is used. These multilayered OLED systems comprise—inter alia—charge-transporting layers, such as electron- and hole-conductor layers, and layers which comprise light-emitting components. These multilayered OLED systems are generally prepared by the successive layer-wise application of polymer solutions which comprise polymers having the various functionalities, and crosslinking of the respective polymer layer applied in order to make it insoluble before the next layer is applied. Such processes are described, for example, in EP 0 637 899 and WO 96/20253.
In the majority of cases, the crosslinking group is bonded directly to a monomer, which then becomes part of a crosslinkable polymer through polymerisation. This preparation route for crosslinked polymers is described, for example, in WO 2006/043087, WO 2005/049689, WO 2005/052027 and US 2007/0228364. The problem associated with the polymerisation of monomers which already carry a crosslinkable group during the polymerisation is undesired crosslinking even during preparation of the polymer. In order to avoid these disadvantages, it is accordingly necessary for the crosslinkable group to remain stable under the polymerisation conditions and not to undergo reactions in order only subsequently to be able to contribute specifically to the crosslinking. Usual polymerisation conditions, such as, for example, in Stille, Suzuki or Yamamoto coupling, require higher temperatures than room temperature. At these temperatures, crosslinkable groups may, even during the polymerisation, undergo undesired side reactions with further crosslinking monomers and/or any further comonomers present. This may restrict the processability of the polymer, result in material defects and lower the performance and/or capacity of the resultant devices. These problems are not satisfactorily solved by the processes used in the prior art.